Criminology
Throughout history, there have been a vast number of recorded accounts of vampires feeding from others in a manner that is either trusting or malicious.  Some of these individuals -- those with ill and selfish intentions -- have been caught by the authorities and punished for their crimes.  Here, I shall present to you a few such cases.  Though are they true vampires?  I suppose it all depends on one's point of view.  See for yourself.
~ The Vampire of Montparnasse ~
Admittedly, the term "vampire" is used inaccurately in this case, as you'll no doubt see why.

In the mid-19th century, the cemetaries of Paris, France -- more specifically, the old public cemetary of Montparnasse -- had a dark cloud hovering over them in the form of a person desecrating the dead that resided there.  The unknown violator was guilty of dismembering, disemboweling, and beheading the corpses, then tossing the individual pieces about in a maniacal frenzy.  The local police made many attempts to somehow trap the one responsible for these heinous acts, only to come up empty-handed since a different cemetary was chosen that particular evening.

Finally, in late June of the year 1849, the dark figure of a man making his way out of a tomb was spotted by a sergeant of the police department and upon the firing of a single gunshot, the officer was certain he had struck him.  The crime scene was searched the very next day and a small, bloodied square that was part of a military uniform was found upon the ground.  This crucial evidence brought the police to the astonishing conclusion that the 100+ desecrations were being committed by one of their own:  Sergeant Bertrand of the 74th Infantry who accepted his arrest very quietly.

During the enquiry concerning the crime he was being charged with, the sergeant -- who was always viewed as a pleasant and handsome individual up to that point -- willingly told his fellow officers of his fetish for playing with corpses, which included such disturbing details as sinking his hands deep into their abdomens, fondling their internal organs, removing the intestines, and squeezing the bodies as he would lay with them.
~ The Monster of Duesseldorf ~
On July 2, 1931, a man was put to death by way of the guillotine at Klingelpirtz Prison in Cologne, Germany.  This person was a well-dressed individual who was respected and soft spoken, never the sort when first glanced upon or even befriended to be thought of as a murderer.  The people who knew Peter Kuerten, who served his sentenced as evidenced by his now headless form, were unable to believe he was actually the person who was dubbed the Monster of Duesseldorf.

This Monster, as he was known by the press, police, and general public, was responsible for numerous attacks which included such horrible acts as the raping, knifing, and throat-slitting of his victims.  He adored not only drinking the blood of those he attacked, but also bathing his hands and face in the crimson lifeforce.

Though many of his victims died at his hands, such as the small girl who was found stabbed thirteen times by a fence, some managed to survive and even escape.  For instance, a woman somehow remained alive after taking twenty-four stab wounds, including some to her temples, although she was unable to reveal the physical identity of her attacker to the authorities.

Apparently, the Monster loved the newspaper coverage for when it wasn't reported that he had murdered another child, he sent forth a letter to the police informing them of the exact location of where he left the young one's body.  The case took an unfortunate turn when the police arrested a man who suffered from epilepsy, but they soon found out that they had the wrong man, for the murders continued while the wrongfully accused was still behind bars.

In the end, it was Peter Kuerten who indirectly identified himself as the ruthless killer by confessing his bloody acts to his wife in order to prove his love to her.  Regretful for keeping the truth from her for so long, he revealed twenty-nine of the murders he was responsible for.  The morning after she learned of the devastating truth, she informed the police.  When they came to take him in, he went willingly and gave a more detailed confession that made all within eye- or earshot ill beyond compare.  In a poor attempt to justify his blood-curdling actions, he wrote letters to his victims' parents during his trial, claiming that his need for blood was similar, if not exact, to other persons' need for alcohol, that he was driven to drink and kill.  During the course of this case, some learned men claimed that Kuerten was a haematodipsiac, a person who had a sexual need for blood.
~ The Hanover Vampire~
One of the most infamous accounts of modern-day vampirism the world has come to know is the case of Frtiz Haarmann in pre-WWII Germany.  Despite being raised in a turbulent household by a drunken, volatile father and a domineering mother, he led a very disciplined life and was seen as a respectful gentleman by the community of Hanover.  He was a graduate of military school and an excellent soldier from the Tenth Jaeger Battalion, which was an army unit that prided itself upon its display of bravery and steadfastness under enemy fire during World War I.  After retiring, reputedly on account of a mysterious illness, he opened his own store:  a butcher shop/delicatessen at 27 Cellarstrasse, which became well-liked for its serving of specialty meats and savories.

While his business was his main focus employment-wise, Haarmann also moonlighted as a police informant.  When performing this "second job," he would frequent the local railway station and search for adolescent boys who were just coming into the city seeking work and a place to stay.  Offering both, he would lure them back to his home and give them a hearty meal before using his large frame to pin them down and killing them with a fatal bite to the neck.  Often times, he would glance upon just the clothes the boys wore in picking whom he would take with him; if anything caught his interest, he would add it to his own attire once he accomplished his goal.  He didn't always act alone.  Many times, a man by the name of Hans Grans would willingly help Haarmann in the choosing of his victims as well as the disposal of the boys' bodies.  It's said that once his victims were dead, he would dismember them and store the separate body parts in various places in and around his residence.

It wasn't until Haarmann's arrest and during his trial that his customers, along with the rest of the Hanover community, discovered the reason for the unusual flavor of his meat.  As it turns out, those that he killed were the source of one of his shop's most well-received delicacies.  With the various body parts of the dead he stored, he stripped the bones of the covering flesh, ground it up, and essentially made human sausages, while the remaining bones were dumped into a canal that ran just behind the deli.  Even the murderer himself was an avid consumer of his horridly-created product.

Though Haarmann admitted to twenty-four murders, the police and many of the Hanover residents believed he was guilty of a much higher number.  The skulls and bones of his unfortunate victims were recovered, but also found were a vast number of other bones which indicated that he did perhaps kill more young men than he said he did.  Regardless of exactly how many lives he took, Fritz Haarmann was executed on Thursday, April 16, 1925.
The information above was derived from the book:
Vampires: From Vlad Drakul to the Vampire Lestat
by Anna Szigethy and Anne Graves
Key Porter Books
ISBN:  1-55263-312-8
As well as the video documentary:
Vampires
(c) 1994 SLC Productions, Inc.
Distributed by Simitar Entertainment, Inc.