Related Clues:

• Worked for the CIA, perhaps
• Had under surveillance
• Noticed
• Caught a glimpse of
• Staked out, say
• Emulated moles
• Watched from seclusion
• Watched from hiding
• Acted the mole
• Bugged, with 'on'
• Was a mole
• Observed secretly
• Did secret-agent work
• Emulated a 29-Down
• Was on a stakeout