UNIX for Advanced & Expert Users

I got the command :
istat filename

shows all the file details like owner and group name.

But
i want to know, who has accessed the file last time.
As istat shows the name of owner of that file and name of the group.

istat does lots of my work but i want to know who has accessed my file last time as there could be 'n' no. of users of that file in a group.
And there is a point that the person who is accessing or recently accessed the file could not be the owner of that file.

I am working on AIX5.0.

Hope you got this !!
Please help me, ASAP !!

Thnaks !!

filesystems don't keep track of who last accessed a file.

Since I'm not an AIX person, as a guess try:
try man wtmp on your system.

Sorry !!

As you said to have a look on man wtmp, its not there in AIX.
Any other solution ??