Russian Security Service head Alexander Bortnikov today announced cryptically that they have zeroed in on some suspects in the assassination of outspoken opposition figure Boris Nemtsov.

"There are always some," Alexander Bortnikov said in response to reporters' questions.

He added that several lines of inquiry are currently pursued by ivestigators, including a possible contract killing. Bortnikov, however, preferred not to reveal much details about the suspects,

Meanwhile, the car used by the assailants in Nemtsov's shooting has been connected to an independent security force that services Goznak, Russia's Finance Ministry. "The Ford car we are talking about does not belong to the Finance Ministry," Goznak's press service said in a statement. Police are yet to find the car.

Nemtsov was an open critic of Russian President Vladimir Putin. He was shot dead on a bridge in Moscow on Friday. The bridge is located very close to Kremlin.

For his part, Putin had condemned the killing, vowing to bring the killers to book. Putin also said that he would personally lead the investigation.

Nemtsov's funeral was held on Tuesday. His final journey was attended by thousands of people. Some opponents of Putin claim that the Russian president was involved in the killing.