Los Angeles - Two men opened fire on a police car patrolling a tough part of Los Angeles, but the two officers inside were not injured and one was able to shoot back, authorities said on Monday. One of the suspects was later arrested and the other is on the loose.The shooting occurred amid heightened tensions over attacks on police elsewhere in the US after grand juries declined to indict white officers in the killings of unarmed black men.Police have not yet determined a motive for the Sunday night shooting in South Los Angeles - an area plagued by gang violence - but said there were no indications it was linked to other attacks on police in the country."It was a complete unprovoked attack," LAPD Deputy Chief Bob Green said initially. "They were just driving on the street, and somebody struck out and tried to kill two policemen."However, Green later said police also were looking into whether the officers might have driven into an ongoing incident and were inadvertently fired at."Last night the initial assessment, based on the reaction of officers and the adrenaline factor, was they were getting ambushed, but, you know, things change and it takes a lot to investigate this," Green said.Officers arrested one man shortly after the attack. Christopher Taylor, 18, was booked on suspicion of shooting at an unoccupied vehicle.An hours-long search followed for the other man, but he remained at large. Police found a handgun and rifle at the scene, and were looking for video evidence and conducting interviews to determine details such as why and how the shooting occurred.The two officers were responding to an unrelated radio call and driving slowly in a neighborhood when they saw two men on a sidewalk and the flash of a rifle being fired, police said.The officers stopped their car, and one got out and returned fire as the men fled. Police found one suspect, uninjured, a short time later along with a rifle and another weapon.Police searched the neighborhood throughout the night for the other suspect, warning nearby residents to stay in their homes. Police stopped the search early on Monday after the suspect was not found.Chief Charlie Beck said at a news conference on Monday that he was concerned that people might be targeting officers but added that the neighborhood had been marred by gang violence during the past several months and there had been a significant number of gang shootings.The shooting comes as protesters in California and across the country have rallied for weeks against police killings of unarmed black men in Missouri and New York.The killing of two New York City officers in their patrol car has departments on edge across the country.The New York gunman ambushed the officers then killed himself after posting threats online, including references to the fatal shooting of 18-year-old Michael Brown in Ferguson, Missouri, and the chokehold death of Eric Garner in New York City. Both were killed by white officers.