Question

Are the verbs of ability correctly used?
1. After participating in many competitions, I could win one of them.
2. Customers could tie the bank robber up.
3. In the end Jack could catch the last train.
4. A lot of the passengers couldn't swim.
5. Many of the witnesses weren't able to be contacted.
6. Laura hasn't been able to work since her accident.

(English isn't my first language, obviously) Thanks for help!

Answer 1

1) yes
2) yes
3) yes
4) yes
5) yes
6) yes 

I'm a bit unsure of 2 and 3, but I hope this helps!