MARTINEZ — A Concord man fatally stabbed in February was blocking the entrance of his home to protect his girlfriend, investigators revealed this week.

Homicide victim Daniel Quast, 53, was standing between his girlfriend and a man who angrily was trying to confront her over a dispute related to a car sale, according to police. Later that day, police arrested Pittsburg resident Eric Martinez, 41, on suspicion of murdering Quast.

Police say that in the early morning of Feb. 22, Martinez arrived at a Concord mobile home park where Quast lived with his girlfriend and demanded his car back, saying Quast’s girlfriend hadn’t paid him for it.

Quast said she had paid him and refused to allow Martinez inside, leading to a fight between the two. A witness reportedly saw Martinez stab Quast multiple times and flee the area, pledging to return with his friends, police said.

Martinez has pleaded not guilty to murder and remains in custody in lieu of $1 million bail. His preliminary hearing date, where a judge will review evidence against him and decide whether to uphold the charges, has not yet been set.

Martinez has more than a dozen felony convictions in Contra Costa County, and in 2009 was acquitted of attempted murder in a stabbing case because of insufficient evidence.