Punt muffed in own end zone (NFL)

[coogrfan]

Some friends of mine and I came up with the following situation(we attempted to answer by checking the digest of rules at NFL.com, without success):

Punt returner attempts to field a punt in his own end zone (I don't know why, temporary insanity perhaps?). The return man muffs the punt(fails to establish possession), and then recovers and is tackled, never leaving the end zone.

Questions
1) What is the correct ruling here, touchback or safety?
2) What would be the correct ruling if the punting team had recovered?
3) If the return man had successfully fielded the punt, fumbled in his own end zone and then recovered the ball, what would be the ruling?
4) Same question as 3), except that the punting team recovers.

Any help would be appreciated. Thanks in advance.