Historical clue formulations

• Looked hard (at) — 2019-10-08
• Studied, with "at" — 2015-02-13
• Looked hard — 2014-05-26
• Used a keyhole, in a way — 2013-07-07
• Looked intently — 2012-01-01
• Squinted (at) — 2009-03-05
• Squinted (at) — 2006-12-24
• Squinted — 2005-02-07
• Looked intently — 2003-04-01
• Looked hard — 2002-12-26
• Looked — 1997-12-07