It's been one month since 21-year-old ASU student Zachary Marco was gunned down while walking home from the library. Tuesday night, police announced arrests in the case.
Three people have been arrested -- but police have only identified two of the suspects.
A third suspect was booked into jail, but his name is not being released -- detectives say they are worried about retaliation.
The suspects allegedly have ties to gang activity. At this time, police have concerns about the third suspect's safety.
Louis Eugene Harper, 20, and Marion Anthony Patterson III, 17, were both formally charged with first degree murder and armed robbery. Bond has been set at $1 million apiece.
Patterson will be charged as an adult. Police say both Tempe men will be provided public
On Oct. 17, Marco was shot and robbed of his backpack, containing a laptop and a cell phone. Witnesses reported seeing two young black men running from the scene, which matches the suspects' description.
Police had no leads to go on, until they found the laptop and discovered fingerprints linking Harper and Patterson to the crime.
Wednesday night, a vigil will be held for Marco. It starts at 6 p.m. at the Honors College on the ASU campus.
The vigil benefits the Zachary Marco Foundation, which provides scholarships for crime victims' families. Marco's father Daniel, a criminal defense attorney, started the foundation after Marco's death.
Marco was studying political science and wanted to go to law school.