You need to file a report on Martha Stein, Carl’s daughter.
Warning: This will result in Carl’s arrest!
The easiest time to do this is after apples become illegal. Government Directive No. 6039 bans red and green apples on September 1 at midnight.
1. Buy an apple from Nathan Kehler, the trader.
2. Plant the apple somewhere in the basement.
3. Search that spot again.
4. Click the evidence line.
5. Submit a report.
Note: There is a quest called “Seasonal Fruit,” where Anna asks Carl to bring her an apple. Do not give the apple directly to Anna, since it won’t trigger the achievement.