Art theft mystery

The actor Max Nail had a party in his house in Hollywood last night. During the party, someone stole a picture in a large frame, but nobody saw anything. The painting was in a locked room and the door was still locked this morning when Max went to get the painting. He was going to lend it to the Museum for a special exhibition next week.

Crime scene:
On the first floor all room's windows were locked exept
a small one. Maybe the thief is a child who can get through
the small window. There were found small pieces of wood
near the window and muddy footprint (size 36) between the
window and the wall where the painting was hanging.

Garden:
There were found the frame of the paining in pieces, a
small, sharp knife and two footprints (size 36 and 44).
S0 the thieves could be two.

Visitors:
*Jake Silversmith- looked at the painting last week
and offered to buy it. He can't be the thief because
he probably had money and he didn't need to stole
it.He isn't the thief.
*Justina Goodman- Max's cousin and poor relation.
Justina asked him for money. She might be the thief
because she hasn't got money but she needs it. If she
stole the paining and then sell it she can earn money.
She could be the thief.
*Frank Constance- Max's neighbour. He is in his
60s. Frank can't be the thief because he is old and
heavy so he isn't able to get in the room trough the
window. Hi isn't the thief.
*Dave Thorman-window cleaner and his daughter (14).
He came at the day of the crime. It was made by two.
Dave is a window cleaner so he had keys for the windows.
Before he went in the house with his daughter he probably
left the window opened. The footprint witch size is 36 must
be his daughter's and the others witch size is 44- his.
Dave and his daughter are the thieves.