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Cold Case Detectives Use Cutting Edge Technology to Track Down and Arrest Germantown Man Believed to

Between August of 2007 and January of 2011 police believe that one man broke into four Germantown and Gaithersburg area homes and raped or attempted to rape women. On Friday, Montgomery County Police announced that detectives from the Cold Case Squad had arrested a Germantown man in connection with those crimes.

At a press conference held Friday afternoon, Montgomery County Police Chief Thomas J. Manger announced that detectives had arrested Marlon Michael Alexander, age 39, of the 13000 block of Dairymaid Drive in Germantown for attempting to commit a sexual offense and for committing three, first-degree rapes in the Gaithersburg and Germantown area from 2007 to 2011. Alexander has also been charged with first-degree burglary in these four crimes as he gained entry into the victims’ homes before sexually assaulting them.

Police said Alexander was arrested on Thursday morning at the Safeway grocery store in the Germantown Central Business District. He will have a bond hearing in Rockville District Court on Monday, Sept. 17.

According to police, detectives have been investigating a series of four burglaries and rapes in which the same suspect left DNA at multiple crime scenes. After obtaining a warrant for and arresting Alexander, a sample of his DNA was taken. Yesterday, the DNA sample provided by Alexander was submitted to the department’s crime lab for analysis. The DNA was analyzed and matched the DNA samples left by the suspect in the four offenses.

Alexander began his series of burglaries and rapes a little over 11 years ago on August 11, 2007, at approximately 1:00 am when police say that he gained entry into the home of a 25-year-old woman, while she was living in the 18200 block of Lost Knife Circle in Gaithersburg. He put an unknown weapon to her head and threatened the victim that he would shoot her if she did not perform a sexual act. A struggle ensued, and the suspect fled from the residence. Police said that the suspect left some DNA evidence at the scene and it was recovered in this case.

The next attack took place three years later on June 19, 2010, when he gained entry into a 68-year-old woman’s home in the 20300 block of Beaconfield Terrace in Germantown at 3:20 am and raped her. The suspect left DNA evidence which recovered in this case.

The next attack took place two months later on August 21, 2010, at approximately 4:15 am, when the suspect forced entry into the 86-year-old woman’s apartment at the assisted living center in the 2100 block of Father Hurley Boulevard in Germantown and raped her. Suspect DNA recovered in this case matched the suspect DNA recovered from the June 19, 2010, sexual assault.

Four months later, police say Alexander returned to the Beaconfield Terrace home of the first 68-year-old victim and raped her again. This took place on January 5, 2011, at 12:45 am. Again DNA evidence matched the DNA evidence from the previous two rapes.

At the press conference, Chief Manger said that detectives used cutting edge technology and persistence to track down the alleged serial rapist.

In June of 2017, cold case detectives sought the services of Parabon NanoLabs, a DNA technology company based in Virginia that specializes in DNA phenotyping: the process of predicting physical appearance and ancestry from unidentified DNA evidence. Using DNA evidence from body fluids left by the suspect at these rape scenes, Parabon’s Snapshot DNA Phenotyping Service has produced what the company and police refer to as a Snapshot composite depicting how the suspect, in this case, may have looked.

Manger also said that using Parabon’s Snapshot DNA and the company’s access to DNA database records from other DNA subscription services such as Ancestry.com or 23-and-me.com, detectives received names of possible family members of the suspect. From those family names, detectives began to do three-weeks of legwork to narrow down the field of possible suspects.

“One of the names that we got was a woman in Georgia,” said Manger. “We spoke with her, and she was able to provide us with information that she did have distant relatives that live in Montgomery County, in this area. From that our officers, with experiences with doing family history and genealogy searches, were able to develop Mr. Alexander as a possible suspect.”

Manger said that MCPD detectives did not have Alexander’s DNA until after a search warrant was obtained. “And we didn’t have the DNA from anyone who submitted it to one of these companies trying to find their family history. What we go were names of people whose DNA analysis was close to what we submitted.”

Manger continued, “It really was the work of the detectives that tracked these folks down, and it was just good fortune — some might say luck that we talked to someone who said that they know we have family in the area. I don’t believe that the woman we spoke with knows or knew the suspect.”

In June of 2017, police released a DNA Snapshot composite sketch based on the DNA evidence left by the suspect at the crime scenes which produce trait predictions for the suspect. Individual predictions were made for the subject’s ancestry, eye color, hair color, skin color, freckling, and face shape. By combining these attributes of appearance, Snapshot composites were produced depicting what the suspect might look like at a certain age and with a certain body-mass index.

Detectives believe it is possible that Alexander committed additional sexual assaults and continue to examine similar unsolved rapes that have occurred in the County, including two in the Germantown/Gaithersburg area.

“We in the 5th District are thankful to the detectives that worked this case and any officer that participated in this investigation,” said 5th District-Germantown Commander, Capt. Mark Plazinski about the arrest of Marlon Alexander. “These are the kind of cases that make me proud to be a Montgomery County Police officer. We don’t give up on a case. It is fantastic for the Germantown community that this person has been taken off the streets. It speaks to the tenacity of our investigators and detectives that they just don’t give up on cases.”


Top: Montgomery County Police Chief Thomas J. Manger announcing the arrest of a suspect in connection with a number of rapes in the Germantown and an attempted rape in the Gaithersburg area which occurred over seven years ago at a press conference.

Next: The suspect Marlon Michael Alexander, 39, of the 13000 block of Dairymaid Drive in Germantown.

Video: Full video of the MCPD Chief Thomas J. Manger’s press conference at Public Safety Headquarters in Gaithersburg on Friday.

Next: The DNA Snapshot composite of the suspect released in June of 2017 which was based on DNA analysis.

Next: The side by-side-by photos of the composite sketch released in 2007 and the suspect mugshot taken after his arrest on Thursday, Sept. 13, 2018

Photos by Germantown Pulse

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