Phoenix police were searching Wednesday evening for Arthur Douglas Harmon, believed to be the gunman who  opened fire in an office complex. Three individuals were shot and one victim, Steven Singer, has been pronounced dead.

The shooting occurred around 10:30 a.m. Wednesday local time. Sgt. Tommy Thompson said Harmon, 72, got into an argument with an unidentified individual which led to Harmon pulling a gun and opening fire, reports The Associated Press.

Two of the three shooting victims have been identified. Singer, 48, was pronounced dead hours after the shooting, while Mark Hummels was identified as one of the victims by his law firm, Osborn Maledon. Hummels was at the office complex representing a client, reports AP. A 32-year-old woman who was wounded does not want to be identified.

Police identified Harmon as he fled the office complex in a white 2013 Kia Optima, reports Hummels and Singer were attending a mediation session when Harmon opened fire and police believe they were the intended targets but are continuing to investigate other possible motives. Said Thompson, “We believe that this individual was probably known to the victims,” reports CNN.

Police soon descended on Harmon’s house, believing that he was at home and armed. Two armored vehicles and a SWAT team surrounded the house, AP reports, but Harmon was not there and is still at large. Schools in the area were closed as a precautionary measure, reports. The shooting took place on the same day that former Arizona Rep. Gabrielle Giffords, who was nearly killed by a gunman two years ago, was testifying in front of Congress for stricter gun control laws.

The Arizona Department of Public Safety has issued an “attempt to locate” bulletin for Harmon. The shooting suspected is described as 6 feet tall, weighing 220 pounds, and was seen in a red shirt and blue jeans, reports KPHO. Police believe he is carrying two weapons.