Serial rape suspect William Costello found dead on second day of his trial in Denver

Costello apparently took his own life

DENVER - After failing to appear in court Thursday morning, an accused serial rapist was found dead in Denver.

William Costello, 48, was supposed to be in court for the second day of his trial for 18 felony counts including sexual assault, sexual assault on a child and kidnapping. A mistrial was declared after his death was discovered.

Costello's body was found at 2890 N. Brighton Blvd. He was out on bond and required to wear a GPS ankle monitor, said Lynn Kimbrough, spokesperson for the Denver District Attorney's Office. The court was discussing Costello's failure to appear when they received word that a body was found wearing that ankle monitor.

Detectives at the scene told 7NEWS the death was an apparent suicide. Police spokesperson Raquel Lopez said the body was taken to a hospital, where death was pronounced.

Costello was first arrested and charged in July 2012 with assault on an at-risk adult following a confrontation between Costello and an anti-abortion activist who was collecting petition signatures.  

Costello’s DNA was taken at the time of his arrest pursuant to Katie’s Law, which requires anyone charged with a felony to have their DNA put into a database.  

The DNA was then linked to three unsolved sexual assault cases occurring in 2008, 2010 and 2011.

Arrest affidavits state that in the 2008 incident, Costello picked up a 13-year-old runaway and sexually assaulted her with a 2-year-old boy in back seat of the car.

In the 2010 incident, a man driving a black Mercedes offered to drive a 22-year-old woman through a Del Taco drive-thru because the dining room was closed, but instead he drove her away.  The report states that he claimed to be a "crooked cop" and sexually assaulted her.  The case was open until a DNA match came back, linking Costello to the crime.

On July 30, 2011, Costello allegedly assaulted a 31-year-old woman in the area of 16th Avenue and Steele Street in Denver.  The two were acquainted with each other through a mutual friend, Morrissey said.

On Sept. 28, 2011, an arrest affidavit states that Costello claimed to be a detective and ordered a 49-year-old woman into his Mercedes. The woman was eventually able to escape the car, but not before being sexually assaulted.


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