DERA ISMAIL KHAN, Pakistan (Reuters) - Pakistan executed its first prisoner in four years on Thursday, hanging a convicted murderer who was a former army serviceman, police said.

Despite the execution of Muhammad Hussain in northwest Pakistan, activists do not expect the country's moratorium on the death penalty to be lifted since this case involved someone in the military. The last execution, in December 2008, also involved the death of a soldier.

Pakistan has more than 8,000 inmates on death row, but a moratorium on executions has been in effect for four years. Pakistani officials say they are working on a draft law to ban the death penalty.

Human rights organizations support the ban, saying that the courts and police in Pakistan are too inept to ensure a fair trial.

"If you look at our investigation system, at the poor quality of the evidence produced in court, how can people get the death penalty on the basis of this?" said Zohra Yusuf, Chairwoman of the Human Rights Commission of Pakistan.

"Most come from underprivileged backgrounds and don't have access to good legal help."

Thursday's execution came after the head of Pakistan's powerful army rejected a plea for clemency, Yusuf said. After the army rejected the plea, the president did not defer the execution, she said.

(Reporting by Saud Mehsud and Katharine Houreld; Writing by Randy Fabi; Editing by Ron Popeski)