SHERMAN OAKS, Calif. (KABC) -- A man in his early 20s was arrested after he allegedly stabbed his two adoptive fathers early Tuesday morning at their home in Sherman Oaks, leaving both of the victims in critical condition, authorities said.According to LAPD investigators, the incident apparently stemmed from an argument involving the suspect, who was home from college for the summer, and his parents. It was unclear what sparked the verbal altercation.Officers responded about 1 a.m. to a report of an assault with a deadly weapon in the 4600 block of Burnet Avenue, where the son was taken into custody without incident. News video from the scene shows him in handcuffs and speaking with police, who described him as cooperative and "nonchalant."Neighbors identified the suspect as 21-year-old Matthew Boulet. Police said he admitted to the stabbings and is facing attempted murder charges.The wounded men, also identified by neighbors as Ken Coll and Tom Boulet, were both transported to a hospital and underwent surgery. The number of stab wounds each suffered was unknown.Detectives recovered a folding pocket knife with a blade measuring 3 or 4 inches, said Lt. Mike Kozak of the Los Angeles Police Department's Valley Bureau.Neighbors who live nearby said they know the victims very well. One woman said the men, an openly gay couple, adopted their son years ago when he was just a boy. She and others are shocked to learn he's been arrested for stabbing them."Whatever happened with Matthew going over the edge like that -- that it's all going to be rectified in some way where everyone will heal," shared neighbor Florence Riggs.Tom Boulet is described as the leader of the local community group."Tom and Ken have been very significant on our block, great models of parenthood," Riggs added.LAPD Lt. Mike Kozak said authorities are investigating reports that there may be mental illness involved with the couple's son.