Take pictures of your son's injuries; bring your son to the doctor to analyze his leg. Get another OP and take temporary custody of kids. Your ex-wife has anger issues with which she needs help.
I just want to make sure I've got the timing down right. It's no biggie, but I'm curious. And I'm piecing this all together from what you've posted and the fact that it's now about 8:00 Easter Sunday a.m. and Avvo says you posted your question about nine hours ago (11:00 p.m. Saturday evening).
So, it sounds like your son came to you around sometime Friday evening, you saw the bruising and took pictures. Then you called the mother. She had excuses and got upset and made some veiled threat against you.
Then, at 1:45 Saturday morning, the police showed up, right? 1:45 a.m.?!?! That would mean that the mother waited a heck of a long time after learning of your concerns before she made the call to the cops. That time-lag would be one thing to point out to any investigators. It demonstrates that the mother wasn't concerned for the safety of the child, but rather was just fueling her anger with you, building up a good head of steam, and then called the police.
As for where to go from here, the other attorneys have the answer: hang on to your kid, take pics, get him to see the doctor, talk with a lawyer, and take appropriate action from there.
Then, All day Saturday went by and you posted you posted your question sometime, late, Saturday evening -- around 11:00 p.m.
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