Solve the case if you are inteligent

Solve  this Case 
A man  was found murdered
on 26.1.1993 afternoon

1. his wife called police,

2.police questioned everyone,

3. Wife: sir, i was sleeping when the 
murder took place

4.Cook: i was cokking

5. Gardener: i was  picking  vegitables,

6.House-maid: i went  to Post office,

7.Children: we went to  play

8. Neighbor : we went to a marriage ,
 police arrested the  murderer

Who is that ?
Give me reason

Answer -House-maid  January  26   post office  is  closed