If you obey the law, you would not keep that information on file once you had determined there was no reasonable reason to keep it on file. You're not allowed to keep that information on a file.
Even now, if you know that someone has been convicted of an offence, for example, and if you have an absolute need to know that--for example, someone has been convicted of impaired driving and you're hiring that person as a driver for your company--you could collect that information because you need to know it. You would not be allowed to collect that information just because you're interested in it, unless you needed to know it for the purposes of your company.