Makin said Mr. Coombes had gone to the police of his own volition.

梅金说库姆斯先生是自己主动去投案的。

《柯林斯英汉双解大词典》

I didn't ask him to go; he went of his own volition.

我没有要求他去，他是出于自愿的。

youdao

It is highly unusual for the forces of Heaven to so directly interfere with man's destiny, but Tyrael was said to act of his own volition.

这种现象极度的不寻常，天堂的力量很少这样直接干预人类的命运，但是泰瑞尔说这是靠他自己的意志决定的。

youdao

Based on what we have seen since November 7th, this is unlikely to happen of his own volition and we need the next Treasury Secretary to push him there.

FORBES: Can Jack Lew Save Obama's Legacy?

In the end, Madoff confessed to his crimes of his own volition to federal investigators, and caught the SEC off guard in regards to both the existence and the scope of the fraud.

FORBES: SEC Refuses to Fire Any Staff Involved with Madoff Debacle

The BBC's Michael Bristow in Beijing says both US and Chinese officials initially said Mr Chen had left the embassy of his own volition, but a more complicated story soon began to emerge.

BBC: Chen Guangcheng left US embassy 'after family threats'