Just because the employee is not coming to duty, does not prove that he has stolen the material.
However, one can take disciplinary action on account of this absence.
#2. Why did he open the CPU ?
Was it for some repairs; and is he entitled to do so ?
If he states that he has not taken the RAM, is it possible that it has been misplaced ?
RAM is a very small component and 1GB/2 GB RAM used in PC's do not have much resale value.
Ascertain the value yourself from the market.
Can an employee risk his job for this ?
Click these links to find the retail price of a brand new RAM :
Page No. 2 - RAM Price List in Nehru Place Market - Latest DDR Memory RAM Price - DDR1, DDR2, DDR3 RAM Price in NehruPlace today
Transcend DDR3-1333/PC3-10600 DDR3 2 GB PC RAM (JM1333KLN-2G) - Transcend: Flipkart.com
You have to find answers to these questions and go over the matter without any prejudice and accordingly ensure that the employee is treated fairly; rather than use the incident to fire him.
Warm regards.