Whose call is this?

[lrpalmer3]

Three person mechanics:

A1 drives to the basket. The drive originates in Trail's primary and contact is made between A1 and B1 on the lay-up. Lead sees charge. Trail sees block.

I've read that the Trail has A1 and the call all the way to the basket if it originates in his primary. I've also read that Lead has the call since it was coming toward him.

Both officials come up with a foul, then make eye contact before signaling. Who takes this call?