Engine locked?

My 04 XC90 vlolvo, 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 timiming belt change, front brakes, front links, change and flush all liquids and 120K service. Took it to my mechanic. He changed the timinng belt, oil change and coolant flush. When I got the car back the engine sounded different. Could hear a tapping noise. He said it will go away. Brought it back twice. !St time he said ti was the lifters and that he suggest I switch to a 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