A short excerpt from the ジョジョの奇妙な冒険 manga. Quick backstory to the aforementioned quote: Dio, who has been adopted into the Joestar family, has been targetting their wealth for years and hopes to inherit it upon the death of his adoptive father. In order to achieve that, he's been a good son ever since gaining his trust over the years and is now trying to realize his goal by poisoning his adoptive father. Jojo, who's actually the real son, has found out about Dio's plans and beat him up for it. The quote is what Dio is thinking right afterwards.
Going from what I know about「～くらいなら／～ぐらいなら」(rather B than A), my first instinct would have been to translate it as "rather than involve the police, I'd start from the beginning", but the やっている is throwing me off. Why is it ている and not やる or やりなおす? My other idea for a translation would be "if I already were to involve the police, I might as well have killed him from the beginning" which sounds more reasonable to me, but it'd kinda go against what I know about「～くらいなら／～ぐらいなら」structurally. I'm also not sure if やる here is the same as 殺る mentioned right before, but since they're so near each other, I could imagine it meaning "to kill" here.
Could anybody help me out here?