Arlington police say a months-long investigation has led to the arrest of a Maryland man accused of planning a violent attack on a county resident — and coming dangerously close to carrying it out.
The Arlington County Police Department announced that Colin Demarco, 26, of Rockville, Maryland, is facing multiple felony charges, including attempted murder and criminal solicitation to commit murder. He was arrested at his home on January 16 and extradited to Virginia. Demarco is now being held without bond at the Arlington County Detention Facility.
What happened on South 7th Street
The case centers on an incident that unfolded on the afternoon of August 10, 2025, in the 3800 block of 7th Street South.
Around 3:15 p.m., police were called after a resident reported a suspicious man on a neighbor’s porch. According to investigators, the man was wearing a surgical mask and rubber gloves, carrying a backpack, and appeared to be hiding a firearm under his shirt.
What made the situation even more alarming: the suspect reportedly approached the witness and asked about the intended victim before walking away.
Police rushed to the scene, set up a perimeter, and searched the neighborhood, but the suspect was gone. Home surveillance video later captured the encounter and became a key piece of evidence.
Digital trail raises serious concerns
Detectives say the real scope of the threat became clear as the investigation moved online.
After executing search warrants for Demarco’s digital records, police say they uncovered evidence showing:
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He had obtained directions to the victim’s home
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He researched firearms owned by a relative
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He possessed written guidance on how to avoid law enforcement detection
Investigators also allege Demarco posted about the victim online and took part in discussions that appeared to encourage others to kill that person. Within days of those posts, police say, he showed up at the victim’s address masked and gloved — possibly armed.
That sequence of events led detectives to seek and obtain arrest warrants.
Charges and what comes next
Demarco is charged with:
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Attempted Murder
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Criminal Solicitation to Commit Murder
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Carrying a Concealed Weapon
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Wearing a Mask in Public to Conceal Identity
Police stress that the investigation remains active. Anyone with information is urged to contact the Arlington County Police Department Tip Line at 703-228-4180.
For residents in Arlington County, the case is a stark reminder of how quickly online behavior can translate into real-world danger — and how crucial it is when neighbors trust their instincts and make the call.