A former US army soldier who murdered 16 Afghan civilians in 2012 has been baptised in prison, and says he prays every day.

In a letter obtained by The News Tribune, Robert Bales – who is serving a life sentence without parole – writes: "I am not an evil man. If you can see past the press clippings and prosecution, you will find someone who loves his family, believes in Christ, would do anything for a friend, and is loyal to a fault."

The letter was written in 2014, two years into Bales' sentence, to I Corps Commander Lt Gen Stephen Lanza, seeking clemency for the killings. Bales was working as a staff sergeant in Afghanistan in 2012 when he shot and killed 16 local civilians, including nine children, in two villages near his assigned camp in Panjwayi, Kandahar province. The incident became known as the Kandahar massacre.

Bales said that he tries to talk or write to his family every day; he has two children, a son and a daughter. His son, four years old at the time, repeatedly asks Bales when he is coming home, he wrote.

"I try to reassure him his Dad loves him so much and I don't know if I'll ever be able to come home. I try to quickly change the subject to Spiderman or the Ninja Turtles, but he always comes back to missing me. I tell him God has a plan."

Bales also said he prays every day for his children: "I dream of holding them in my arms and letting them fall asleep in my arms. I so want to take away their pain and confusion. I pray to God every day for them.

"I pray He gives me a chance to be a father to them or lets me die in my sleep so their wounds can heal."

The letter reveals that Bales has been baptised since being incarcerated at the US Disciplinary Barracks on Fort Leavenworth in Kansas.

"I am doing everything in my power to prove to the Army and the world that I deserve another chance," he wrote. "I volunteer to clean the latrines in the Chapel on Tuesdays and work the sound equipment every third Sunday. I have been baptized since arriving at the USDB, as well as earning certificates for completing...several religious classes.

"Sir, I am not a threat to society, I just want to go home and be a husband and a father."

In a further impassioned plea for mercy, Bales says that he was "consumed by war" as a soldier, and is now haunted by the faces of those he murdered; even naming all 16 from the incident in Kandahar. "The truth is I pray for all the people I have killed in war. War is ugly. I hate myself for my part in the war," he wrote.

"Paul (an apostle of Christ) tells us in Romans 12:20 if you enemy is hungry, feed him. If he is thirsty, give him something to drink. Sir, Paul tells us later to not be overcome by evil, but overcome evil with good."

On Friday, an Army spokesman said that Bales' request to have his conviction overturned was rejected. The case will now be sent to the Army Court of Criminal Appeal.