04 XC90 engine failure

My 04 XC90 Volvo, 5.2T AWD, 127K miles engine ceased. 5 days prior my Volvo dealership gave me a complimentary complete diagnostic. No engine problem was noted. Recommended timing belt change, front brakes, front links, change and flush all liquids and 120K service. My mechanic changed the timing belt, oil change and coolant flush. When I got the car back the engine sounded different. Could hear tapping noise. He said it will go away. Brought it back twice. 1st time he said it was the lifters and that he suggest I switch to heavier oil. Engine still does not sound right, brought it back the next day, this time he bought an additive that he poured in the engine. The very next day my engine truck died in the HWY. I had it towed to his shop and he said the engine ceased. And that the crankshaft broke. My question is, is the mechanic liable for this? I told him my truck was fine until you messed with it. He is saying that changing timing belt will never cause an engine to cease even if done wrong. Please I want to know my next step. Thanks

The Gates site shows the 5 cylinder motor is not an interference motor, and the 6 cylinder motor is an interference motor. If your XC90 has the 6 cylinder motor it could most certainly lock up if the timing belt fails. While less likely a defective water pump or belt tensioner could give out and lock up the 5 cylinder also but that would be more easily repaired.

It looks like more investigation into why the motor locked up is needed, meaning start tearing down the motor with the first area being the timing belt parts. My gut says the timing belt job was botched, either a bad part, an old part reused (such as a bolt) sheared off and failed, or simply bad mechanic botched the job.