Montgomery County

‘DNA Gave Us a Break:' Genealogy Tools Lead Montgomery Co. Police to Cold Case Rape Suspect

The victims are an 86-year-old woman, 68-year-old woman and 25-year-old woman

Montgomery County police have arrested a 39-year-old man in connection with a series of rapes that took place in the county between 2007 and 2011.

Marlon Michael Alexander of Germantown was arrested at a grocery store Thursday, just hours after his DNA was matched to four crime scenes, police say.

Police tracked down Alexander after a DNA database search turned up two relatives, at least one of whom helped police in the investigation.

In each case, police say Alexander broke into a woman's home and sexually assaulted her. 

The first attack occurred on Aug. 11, 2007 in the 18200 block of Lost Knife Circle in Gaithersburg. Police say Alexander broke into the 25-year-old victim's home and told her he would shoot her if she did not perform a sex act. 

The two struggled before the suspect left the home, police say. 

Three years later, on June 19, 2010, police say Alexander broke into the Germantown home of a 68-year-old woman in the middle of the night. He held a weapon to her head and raped her, according to investigators. 


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Just over a month later, police believe Alexander broke into the home of an 86-year-old woman who was living at a senior living facility in Germantown. Police say he was armed with a pair of scissors when he raped her. He struck the woman multiple times before leaving, according to police. 

On Jan. 5, 2011, police say the victim of the June 19, 2010 incident was attacked again when Alexander once again broke into her home. 

"The second time, he came into my bedroom window feet first but as soon as he hit the ground and we looked at each other we knew,” the victim said in an interview with News4 in 2011. "I probably said something like, 'You again.'"

The 86-year-old died before her attacker was caught, but the two other victims are aware of the arrest and prepared to help in the prosecution, police said.

Investigators say DNA collected at all four crime scenes matched. But it didn't lead investigators to the suspect until a Herndon-based company called Parabon NanoLabs compared the sample to their database, Montgomery County Police Chief Thomas Manger said.

Parabon contracts information from firms that offer DNA testing for genealogy and similar purposes, Manger said. Last year, the company used the suspect's DNA to render a composite sketch based off his genetic fingerprint.

The company also compared the suspect's DNA to their database. Two names popped up. Parabon scientists told investigators they were likely relatives.

One of those relatives, a woman living in Georgia, confirmed that she had relatives in the Montgomery County area. She helped police look in the right direction, even though she was distant from Alexander.

"I don't think the woman we spoke with knows or knew the suspect," Manger said.

From there, Manager said, an officer well-versed in family history and genealogy began digging through census records and obituaries to build a family tree.

Alexander, who also fit the description given by the victims and the composite, was identified as a possible suspect.

Detectives obtained Alexander's DNA using a search warrant. Hours after his DNA was analyzed and matched, Alexander was arrested at a grocery store in Germantown. 

"The use of genealogy and DNA gave us a break in this case," Manger said.

Police believe he may be responsible for other sexual assaults in the county. He has long lived in the area of Gaithersburg and Germantown, Manger said.

Alexander is being held without bond. 

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