Solution to 17A has been deliberately left unsolved and is to be answered by a non-regular/novice commenter, with proper annotation. Those who have answered earlier in the week, please give others a chance.
Open for anyone to answer, if not solved by 1 PM.
ACROSS
1 American throttled by armed culprit violently - it could result in death penalty (7,6) CAPITAL MURDER {A} in {ARMED+CULPRIT}*
8 Brief, sporadic fights (5) SPARS SPARSe
9 Falls down badly, loses consciousness primarily after consuming drink (9) COLLAPSES {LOSES+Co...s}* over {LAP}
11 Revives tipsy marines with tea (10) REANIMATES {MARINES+TEA}*
12 Fun in Gujarat's first sanctuary (4) GLEE {Gu...t}{LEE}
14 Support copper beginning to berate beastly youngster (4,3) BEAR CUB {BEAR}{CU}{Be...e}
16 Gasp about diamond's size (7) BREADTH {BREA{D}TH}
17 Finest century, extremely impressive in final (7) L?C?E?T (Addendum - LACIEST {LA{C}Im...vE}ST} - See comments)
19 Involve head of radiology in treatment of emboli (7) EMBROIL {EMB{Ra...y}OIL*}
22 Moving injured girl at once (10) RELOCATING*
25 Remove coach after losing one game (9) TRANSPORT {TRAiN}{SPORT}
26 Lyric poet in neighbourhood is terrific (5) ODIST [T]
27 Forbid foolish attendant picking up dope for transient visitor (4,2,7) BIRD OF PASSAGE {FORBID}*{P{ASS}AGE}
DOWN
2 A Tibetan monk embracing a bishop in American state (7) ALABAMA {A}{L{A}{B}AMA}
3 How patient after surgery might be laughing uncontrollably (2,8) IN STITCHES [DD]
5 Supple batter turned and smashed ball over English umpire's foot (9) MALLEABLE {LAM<=}{L{E}ABL*}{u...rE}
6 Stern parent (4) REAR [DD]
7 Stored fodder in citadel is nearly over (7) ENSILED [T<=]
8 Flasher in spot, without pants or belt (6,5) STROBE LIGHT {S{OR+BELT}*IGHT}
10 Find out and be incensed by drunk husband chasing girl inside (3,3,5) SEE THE LIGHT {SEETHE}{LI{H}<=>{G}T}
13 Like a film with some new rumba moves (10) MEMBRANOUS {SOME+N+RUMBA}*
15 Gambler turned richer (6,3) BETTER OFF {BETTER}{OFF}
24 Exercised in shade, Sun's coming up (4) USED [T<=]
Reference List
American = A, Diamond = D, Century = C, Bishop = B, Cocaine = C, English = E, Husband = H, Girl = G, New = N, Church = CE, Mass = M, Island = I