Daniel J. Leahy common name checked by Invelos credit lookup.

CLT results:
Daniel J. Leahy is credited in 161 titles (361 profiles)
Daniel Leahy is credited in 127 titles (362 profiles)
Dan Leahy is credited in 105 titles (280 profiles)

movies.nytimes
hollywood.com
Inbaseline
imdb

I'm trying to check the CLT

Daniel J. Leahy 4
The Breakfast Club (verified by tweeter)
Daylight (verified by antolod)
The Fast and the Furious  (verified by Giga Wizard)
Mallrats (verified by me)

Daniel Leahy 20
City of Ember (verified by Forget_the_Rest)
Dazed and Confused (verified by tweeter)
Die Hard with a Vangeance (verified by me, confimed by Giga Wizard)
Double Dragon (verified by Giga Wizard)
Dragnet (verified by me)
Dragonheart (verified by Merrik, confirmed by antolod)
The Dream Team (verified by T!M)
Fletch Lives (verified by ninehours)
Harlem Nights (verified by T!M)
Hustle & Flow (verified by tweeter)
K-9 (verified by T!M)
The Mummy: Tomb of the Dragon Emperor (verified by antolod)
October Sky (verified by tweeter)
Scooby-Doo 2: Monsters Unleashed  (verified by reybr)
Stay Alive (verified by Giga Wizard)
Tears of the Sun (verified by tweeter)
Training Days (verified by northbloke)
Troop Beverly Hills (verified by T!M)
Untraceable (verified by Merrik)
xXx (verified by Giga Wizard)

Dan Leahy 20
Anaconda (verified by Merrik)
Back to the Future (verified by me)
Ballistic Ecks vs Sever (verified by me, confimed by Giga Wizard)
Cats & Dogs (verified by ninehours)
Cutthroat Island (verified by reybr)
Dudley Do-Right (verified by T!M)
Fracture (verified by Giga Wizard)
The Girl Next Door (verified by Merrik)
For Richer or Poorer (verified by T!M)
Halloween (verified by northbloke)
John Carpenter's Vampires (verified by Forget_the_Rest)
Kiss Kiss Bang Bang (verified by northbloke)
Midnight Run (verified by T!M)
Pathfinder (verified by ninehours)
Pollock (verified by Merrik)
Safe Men (verified by T!M)
The Skulls (verified by Forget_the_Rest)
Summer Catch (verified by reybr)
Three Kings (verified by me)
Virus (verified by Giga Wizard)

CLT to check:
In green the credits confirmed by the Academy of Motion Picture Art and Sciences Web Site

Daniel J. Leahy [Daniel Leahy] or Daniel Leahy 11
An American Tail: Fievel Goes West (Daniel J. Leahy [Daniel Leahy] in CTL)
Sweet November (Daniel J. Leahy [Daniel Leahy] in CLT)
The Final Season (Daniel Leahy in CLT)
Heartbreak Hotel (Daniel Leahy in CLT)
Kull the Conqueror (Daniel Leahy in CLT)
McHale's Navy (Daniel Leahy in CLT)
Mobsters (Daniel Leahy in CLT)
Shout (Daniel Leahy in CLT)
Teenage Mutant Ninja Turtles III (Daniel Leahy in CLT)
Till We Meet Again (Daniel Leahy in CLT)
Timebomb (Daniel Leahy in CLT)

Daniel J. Leahy [Dan Leahy] or Dan Leahy 8
Hardball (Daniel J. Leahy [Dan Leahy] in CTL)
Mr. Woodcock (Daniel J. Leahy [Dan Leahy] in CLT)
Summer Catch (Dan Leahy in CLT)
Dancing at the Blue Iguana (Daniel J. Leahy [Dan Leahy] in CLT)
Gilmore Girls: Season 1 (Daniel Leahy [Dan Leahy] in CLT)
SeaQuest DSV: Season 1 (Daniel J. Leahy [Dan Leahy] in CLT)
Overnight Delivery (Dan Leahy in CLT)
Swan Princess: The Mystery of the Enchanted Kingdom (Dan Leahy in CLT)

Daniel J. Leahy 4
Major Payne (Daniel J. Leahy in CLT)
Mister Cool (Daniel J. Leahy in CLT)
Problem Child (Daniel J. Leahy in CLT, Daniel  Leahy for Academy of Motion Picture Art and Sciences)
Problem Child 2 (Daniel J. Leahy in CLT, Daniel  Leahy for Academy of Motion Picture Art and Sciences)

Ambiguous 3
Flipper (Daniel J. Leahy and Daniel Leahy in CLT, Daniel Leahy for Academy of Motion Picture Art and Sciences)
The Rat Pack (Daniel J. Leahy and Dan Leahy in CLT, Daniel J. Leahy for IMDB)
Torque (Daniel J. Leahy and Dan Leahy in CLT, Daniel Leahy for Academy of Motion Picture Art and Sciences
and Dan Leahy for IMDB)

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Training Day: Daniel Leahy
Kiss Kiss Bang Bang: Dan Leahy

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Quoting ninehours:

Quote:
Just checked Superman: The Movie but could not find a credit for him but according to IMDb he was part of the 2000 restoration crew

He's credited as Daniel Leahy under the Film Restoration credits of the Donner Cut
These credits aren't on the theatrical print so he shouldn't be listed on those profiles.

Halloween: Daniel Leahy

Breakfast Club: Daniel J.
Dazed and Confused: Daniel