1970s does make a bit of a difference. Glad you have amended the year in your initial post.
I would search for Peter’s death certificate. Death certificates for the 1970s are not on-line. They are accessible, just not on-line. If you can get to GRONI or PRONI in Belfast, you can look them up. If you can’t get there in person you can either e-mail or phone GRONI and ask them to search for you (there may be a search fee) or you could get a researcher to do it for you. Researchers in the PRONI area: http://sgni.net
Once you have found the date of death, you may be able to search for a probate file for Peter too. (PRONI has those). Again they are not on-line – for the 1970s anyway – but a researcher can look it up for you. The probate file should contain information about next of kin, and if Peter left a will, then that may prove helpful in identifying close family.
There is likely to be a coroner’s report too, but that is probably closed at present, as the event was within the past 100 years.
With a date of death you also might search local newspapers for a report on the accident. Copies of most newspapers in Northern Ireland are held in Belfast Central Library. (Personal visit required to view them).